Abstract : Encryption ‘distributing over pairs' is a technique employed in several cryptographic protocols. We show that unification is decidable for an equational theory HE specifying such an encryption. The method consists in transforming any given problem in such a way, that the resulting problem can be solved by combining a graph-based reasoning on its equations involving the homomorphisms, with a syntactic reasoning on its pairings. We show HE-unification to be NP-hard and in NEXPTIME.